The project has two major objectives. The first is the application of a number of standard investigations to a large number of cases of leukemia and other myeloproliferative disorders in both the untreated phase and during the course of therapy. This screening protocol is designed to provide detailed information available for patient diagnosis and to assess responsiveness to therapy. The second major objective evolves from the screening program and is aimed at the investigation of (1) the nature of the cellular and regulatory lesions in leukemia and other hemopoietic disorders; (2) the interaction between normal and leukemic populations during the development and treatment of leukemia.